| Battery FAQ
What is over-charge? What are impacts result on cells performance?
The continual charge action after fully charged with certain charge approach is overcharge.
For Ni-Cd cell, while overcharged the following reactions are generated:
Positive 4OH- - 4e -> 2H2O + O2
Negative 2Cd + O2 -> 2CdO
Because the positive capacity is higher than the negative on design, the generated oxygen in positive can composite, through separator, with Cd generated in negative. In general condition the internal pressure will not rise obviously, but if the charge current is so heavy or the charge time is so long, and the generated oxygen can not be used up in time, there will be some quality defect risen such as internal pressure rising, battery distortion, leakage and so on. Meanwhile its performance will decline.
What is over-discharge? What are impacts on cell performance?
If a cell's voltage reaches a designed value, that means the battery has discharge the stored capacity, but still the discharge action is continual, over-discharge will cause. Commonly the end voltage can be identified through discharge current, for example the end voltage is set at 1.0V/cell as discharged at 0.2C-2C, and 0.8V/cell at 3C or more, e.g. 5C or 10C. Overdischarge may cause disaster, especially at heavy current or repeated overdicharge. Commonly overdischarge can make cell inner pressure raise, and the reversibility of activity materials both in positive and negative will be damaged. Even by charge only part can recover and the capacity is reduced obviously.
How many are there charging control methods?
In order to protect being overdischarged, it is necessary to control the end point of charge. When the cell is fully charged, some special appearances can suggest the charge is final¡£ Usually there are 6 methods:
1) Peak voltage: measuring a cell's peak voltage can tell charge is end.
2) dT/dt control: measuring a cell's peak temperature change ration can tell the charge is end.
3)T control: the temperature difference between the cell and the ambient as the cell is fully charged will be the biggest.
4)-dV/dt control: as the cell is fully charged, its voltage will drop to a certain value.
5)Time control: generally the time which takes necessarily to charge 130% nominal capacity is set to control the end of charge.
6)TCO control: Considering the cell safety and characteristic,it will avoid being charged under high temperature(exception HT cell).So when the cell temperature reaches to 60oC high,charge will be stopped. What is the best condition for cells store?
In accordance with IEC,the cell should be stored under temperature 20±5oC and humidity(65±20)%. Commonly temperature is higher, while capacity retention is lower, and vice versa. The best place to store a cell is in a refrigerator with a temperature range of 0oC-10oC, especially for primary batteries. While for secondary batteries, their loss of capacity during storage, may be better compensated by recharging. How long can a cell be stored?
On theory energy loss can't be avoided during store. Its proper electrochemistry construction makes the losing unavoidable. Self-discharge is the best-known causation. Generally this has to do with the electrolytic solubility of the positive electrode material or its thermodynamic instability (easy spontaneous decomposition). Self-discharge in rechargeable batteries is particularly high in comparison to primary battery. Furthermore every month a battery self-discharge rate is various depending on the system. It changes in the range of 10-35%. Primary battery self-discharge is lower considerably. At room temperature it may even be below 2%. However, various processes take place in parallel with this which lead to an increase of the battery's internal resistance during storage. These processes lead to a reduction in load capability. However energy loss is more noticeable at relatively high discharge current. The below table lists self-discharge approximation under normal storage conditions:
Type -----------------------Self-discharge
Alkali manganese(MnO2/Zn), cycloidal <2%
Zinc carbon(MnO2/Zn), cycloidal <4%
Li-ion(LiMnO2),cycloidal and button cell approx 1%
Ni-MH/Ni-Cd cell <35% What are the voltage of difference cell types and the usage area?
type voltage application area
SLI(engine) 12V automobile, commercial vehicle, motorcycle
Li 6V cameras
LiMn button 3V pocket calculators, watches, remote control devices
Silver oxide button 1.55V wrist watches, small clocks
Alkali manganese 1.5V portable audio equipment, cameras, games
Alkali manganese button 1.5V pocket calculators, electronic devices
Zinc carbon cycloidal cell 1.5V larms, flashlights, toys
Zinc air button cell 1.4V hearing aids
MnO2 button cell 1.35V hearing aids, cameras
Ni-Cd 1.2V power tools, camcorders, mobile telephones, cordless telephones
Ni-MH 1.2V mobile telephone, cordless phone, portable cameras, notebooks, emergency lights, house applications
Li-ion 3.6V mobile telephone, notebooks What impact may an ambient temperature have on battery performance?
Low temperatures (e.g. -15oC) will obviously reduce Ni-Cd and Ni-MH battery discharge rate. At -20oC electrolyte is at its freezing point, charge speed will greatly slow down. At low temperature (under -15oC ) charge will raise the internal gas pressure and probably unseal the safety vent. Ambient temperature of 5oC to 30oC is the best range to get effective charge. Generally with temperature rising charge efficiency will become higher. But when the temperature rises to 45oC or higher, the materials performance in the battery will be degenerated and battery service life will be shorten greatly. What a battery short circuit and its consequences?
Any kinds of conductive material being bridged with the external terminals of a battery will result in short circuit. Based on the battery system, a short circuit may have serious consequences, e.g. rising electrolyte temperature or building up internal gas pressure. If the internal gas pressure value exceeds the limitation of cell cap endurances, the electrolyte will leak, which will damage battery greatly. If safe vent fails to respond, even explosion will occur. Therefore don't short circuit. What is memory effect?
Memory effect only happens on Ni-Cd batteries. As in traditional technology a Ni-Cd battery's negative is agglomeration with thick Ni crystal, if Ni-Cd batteries are recharged before they have been fully discharged, Ni crystal easily gathers to form agglomeration, which makes the primary discharge platform come into being. The battery stores the platform, which will be considered as the end of discharge for the next cycle even though the capacity decides that the battery can be discharged to a lower platform. The battery will store this process in its memory so during the next discharge, the battery only remembers this reduced capacity. Similarly any further incomplete discharge in each use will aggravate the effect makes lower capacity. The effect there are two methods to remove the effect: firstly deep discharge at trickle current (i.e. 0.1C to 0V), secondly several cycles at high currents (e.g. 1C). What impact is the battery on environment?
Nowadays almost available batteries are free from Hg. But heavy metals are still essential components in Hg battery, rechargeable Ni-Cd battery, and lead-acid battery. If disposed of improperly and in large quantities these metals may damage the environment. Internationally at present special institutions have been existed to collect the used batteries such as oxidation mercury, Ni-Cd, lead-acid. OCEANSUN has been making great efforts to develop environmental benign batteries such (Ni-MH and Li-ion) to replace Ni-Cd.
What are the possible reasons to cause 0V or low voltage?
1) Batteries are external short-circuited or overcharged, reverse charged (forced over-discharge)
2) Continually being overcharged at high rate current will cause electrode pole expand and positive poles touch directly.
3) Internal or slight short circuit, e.g. burrs in positive and negative plates touch together if penetrated through separator, or positive and negative plates are wrongly placed causing the two plates to contact together, or the positive plate gets in touch with the outside steel case, or negative material fall into separator, or separator is defective, or positive current collector contacts with negative plate. Why do batteries packs with 0V or low voltage happen?
1) One of the cells voltages is 0V.
2) Plugs are short or open circuit, or ill touched.
3) Lead wires are broken from the soldering or weakly soldered.
4) Wrong battery connection or the connection tabs are miss or weak weld or broken off.
5) Inner connections of the assembly compositions are wrong or damaged. What are possibly the reasons cause cells or battery packages unchargeable?
1) 0V cell low voltage cell in packages.
2) Wrong battery connection, or abnormity inner parts or circuit protector
3) Charger is failure to output current.
4) External factors can be possible triggers of extremely low charge rate (e.g. extremely low or high temperatures). What are possibly the reasons cause cells or battery packages can't discharge?
1) Storage will shorten its service life.
2) Not be fully charged or not be charged;
3) Excessively low ambient temperature;
4) Low discharge efficiency, for instance at high current discharge, inside materials of ordinary battery will diffuse, and the reaction speed can't follow, that will cause the voltage toboggan and the battery can't discharge. Cells or batteries with short discharge time, what is the reason?
1) Battery is not fully charged, such as inadequate charge time, lower charge efficiency and so on.
2) Excessively heavy discharge current will result shorter discharge time of low discharge efficiency.
3) Discharge excessively low ambient temperature will descend discharge efficiency.
Battery bottom plumping up, belly protruding, even leakage, what are possibly the causes?
1) Batteries are overcharged especially at continuous high rate current.
2) Batteries are forced to over discharge.
Why the battery service life is short?
1) Charger or charge circuit does not matched to battery system.
2) Over charged or over discharged.
3) Battery systems are not consistent with appliances. What will happen if cells with different capacity are packed together?
If different capacity cells or mixing fresh and old cells were used, leakage or zero voltage would occur. That is because when charge, some cells with high capacity cannot be fully charged, while the others with low capacity will be overcharged due to the different capacity. While discharge high capacity cell can't be fully discharged, however the low one is over discharged. If repeated like so, the cells would be damaged to leakage or low (zero) voltage. Can the cell be remained in the application without using for a long period or after being used?
If the application is not in use for an extended period of time it is better to remove the battery from the application and to store in a dry and cool place. If this is not done, a minimum amount of current will continue to be taken out of the battery by the application, even if the application is switched off-which may shorten the battery's service life.
A cordless telephone should be put back onto the base after each use
According to usual practice and the cordless phone design, the phone should be put back onto the base after each use so that the battery was activated to makeup the discharged capacity and the losing capacity of self-discharge. But occasional complete discharge is recommended to recover the battery to its initial capacity and discharge character. Properly it is better to take the battery out, and keep it open circuit, charge it when reuse. Why the temperature hoik and the voltage decrease at the end of charge?
Continue to charge is an overcharge procedure when a battery has been fully charged. At this time the Ni(OH)2 of positive electrode had become NiOOH, the battery voltage reaches a balance value(maximum value). Continued charge will oxide OH- into oxygen:
4OH- - e -> O2 + 2H2O + heat
The formed oxygen permeate separator and compound with cadmium of negative electrode:
2Cd + O2 -> 2CdO + heat
This chemical combination reaction generates large amount of heat, so the temperature of total battery system increases sharply. The more high temperature, the more low balance voltage, that is temperature increases will lead to balance voltage decreases, so the battery voltage will decrease after it had been fully charged. What are the advantages and shortcomings of protection elements of battery?
Follow table compare their performance several familiar protection elements of battery:
Name Main Materials Function Advantage Shortcoming
Temperature- controlled switch PTC Large current protection Induce the current and temperature change quickly, too high temperature or too large current will make the temperature of double metal parcels in switch reaches its rated value, the double parcels break quickly, so the circuit is protected. The metal parcels may not set and the battery can't work any more.
Polyswitch PTC Large current protection The impedance of the element increases linearly when its temperature increase, and its impedance will increases sharply if the current or temperature reaches a specified value, so the current will decrease to several mA level. When the temperature decreases to normal level, the element can recover to initial state. It can be used to assemble battery as a connect parcel. High cost
Fuse Induce the current and temperature of circuit Fuse will melt to protect the electrocircuit if the current or temperature reaches a specified value. Fuse can't recover after melting , and need replace it in time, this is a trouble. What is the influence of temperature on battery performance in general?
Of all environmental factors, the temperature has the greatest effect on battery charge and discharge behavior. This has to do with the temperature-dependent electrochemical reactions occurring at the electrode/electrolyte interface, which may be considered the heart of the battery. If the temperature decreases, the rate of electrode reaction decreases too. Assuming the battery voltage remains constant, the discharging current drops and thus the power output of the battery. The opposite effect occurs if the temperature rises, i.e. the power output of the battery increases.
The temperature also affects the speed of transport processes within the electrolyte and its porous electrode. A rise in temperature accelerates transport processes, a decrease in temperature slows them down. The charge / discharge performance of the battery may also be affected. But if the temperature is too high ( more than 45oC), battery cycle life will short sharply due to the active materials decline and electrolyte exhaust.
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